(1) Field of the Invention
This invention relates to the method of depositing thin films as a means to apply safe permanent human and/or machine-readable identification markings to the surfaces of materials that do not outgas in a vacuum environment, and specifically to apparatus for applying these markings.
(2) Description of the Related Art
Industry utilizes part identification markings to identify parts and components. The use of machine readable binary codes in the form of matrix representations is described in U.S. Pat. No. 5,380,415. A wide range of marking methods has been developed for his purpose including means to apply machine-readable symbols used for automatic data collection. These methods involve the use of attached identification means such as adhesive backed labels and tapes, bands, tags, identification plates and direct part markings (DPM) which are applied to, or formed by altering a surface of a part.
DPM is generally recommended in applications where: 1) traceability is required after the product is separated from its temporary identification, such as marked packaging, 2) the part is too small to be marked with a bar code labels or tags, or 3) the part is subjected to environmental conditions that preclude the use of an attached identification means that will not survive those conditions.
DPM can generally be subdivided into two general categories: non-intrusive and intrusive. Intrusive marking, methods alter a surface by abrasion, cutting, burning, vaporizing or other destructive means. Intrusive marking methods include methods such as micro-abrasive blast, dot peening, electrochemical etch, machine engraving, milling, laser etching and engraving or other similar marking methods.
Non-intrusive markings, also known as additive markings, can be produced as part of the manufacturing, process, such as cast, forge or mold operations, or by adding, a layer of media to a surface using methods that have no adverse effects on material properties. Examples of additive markings would include ink jet printing, silk screening, stenciling or other similar marking methods.
While both non-intrusive and intrusive marking methods are widely used in industry, their applications are limited. Non-intrusive markings are not generally used in applications associated with harsh environments. For instance, ink marking would not be used to mark engine components because the high heat experienced by the part would burn off the marking media. Intrusive markings, which are designed to survive harsh environments, may be considered to be controlled defects in high stress applications and could degrade material properties beyond a point of acceptability.
Some intrusive markings, especially those done by lasers, are generally not used in safety critical applications without appropriate metallurgical testing and engineering approval. Safety critical applications include parts whose failure could result in hazardous conditions. Examples of safety critical applications include systems related to aircraft propulsion, vehicle control, equipment handling, high pressure, pyrotechnics, and nuclear, biological and chemical containment applications. An example of an inappropriate use of an intrusive marking would be the laser etching of an engine turbine blade in a critical stress location. Although safe settings could be established through metallurgical testing, there remains a risk of input errors when entering settings. For example, an input error made during a turbine blade marking operation could result in the application of a mark that is applied with too much heat, resulting in micro-cracks that could propagate under stress over time. Unknown defects in engine blades could result in part failures leading to catastrophic engine loss and subsequent loss of aircraft and personnel.
The aerospace industry has been seeking new marking methods that are safe and that can withstand harsh environments. The National Aeronautics and Space Administration (NASA) investigated a number of methods to spray and bond particles consisting of atoms and ions of source material onto surfaces. These included plasma-activated chemical vapor deposition, laser chemical deposition, sputtering, cathode-spot arc coating, electron beam evaporation deposition, ion plating, arc evaporation and cathode arc plasma deposition. However, all of the known processes tend to have relatively slow deposition rates compared to non-vapor coating methods. Consequently, NASA developed a Vacuum Arc Vapor Depression (VAVD) apparatus, as described in U.S. Pat. No. 5,380,415, consisting of a vacuum chamber system for producing vapor deposits. It utilizes the arc formed in a gas flowing through a hollow tungsten electrode in a substantially vacuum environment. The VAVD process is capable of high deposition rates and produces no hazardous wastes or by-products.
Tests conducted using the VAVD apparatus produced high quality thin film coatings including small, high fidelity human and machine-readable part identification symbols in seconds. This activity however, was deemed impractical for use because the size and operation of the vacuum chamber limited both the size and volume of parts being marked and required operation within a vacuum chamber.
Consequently, it is a primary object of the present invention to provide a marking apparatus and method that can be used to produce human and/or machine readable identification markings by applying thin films of material onto surfaces using Vacuum Arc Vapor Deposition technology.
Another object of the present invention is to provide a means to apply thin film deposition identification marks to a surface using a mask to form a representation of a human or machine-readable part identification symbol, said symbol preferably being a Data Matrix Symbol.
A further object of the present invention is to provide a means to apply a thin film identification mark of contrasting color to a surface, the area of which is limited to the size of the desired mark, that is subsequently selectively removed using a separate device that becomes a marker, such as a laser, to form a representation of a part identification marking symbol, the symbol marking being captured and decoded using an optical reader fitted with a light detector like a charged-coupled device (CCD) or complementary metal-oxide semi-conductor (CMOS).
A still further object of the invention involves the addition of a removable coating to a surface, the area of which is limited to the size of the desired mark, using ink jet, laser bonding, or similar marking technique to form a mask to block the VAVD coating process, said coating being subsequently removed to expose a representation of a part identification symbol or other desired marking.
It is yet another object of present invention to provide a thin film coating applied to a surface, the area of which is limited to the size of the desired mark, that exhibits a difference in density, reflectivity, absorption or other variance to promote the capture and decoding of a part identification marking, using a image sensing reader, said sensing means including but are not limited to, capacitance, magneto-optic, micro-power impulse radar, thermal, IR, x-ray, and ultrasound.
Still another object of the present invention provides a symbol which represents a human and/or machine readable identification marking, and which exhibits a difference in density, reflectivity, absorption or other variance which is optionally covered with a coating so as to hide the mark for aesthetic or security reasons and then capturing the symbol with a sensing reader and decoder to yield human-readable information.
The present invention relates to a method and apparatus for applying symbols by using VAVD technology. The apparatus may be a hand-held device or mounted to a robot or fixed station. The apparatus is adapted to be used in a manufacturing or other environment. The apparatus preferably contains a housing. The housing contains a chamber housing an electrode, a charge and a vacuum port fixed with a deformable nozzle. A mask is placed between the nozzle and a substrate to be marked. With the nozzle sealed against the mask and/or substrate, a vacuum is drawn in the chamber. Next, the charge is at least partially vaporized by the electrode allowing the vapor to deposit on the portion of the substrate exposed through the mask. The apparatus may be hand-held or may be a fixed component in a manufacturing facility or other location. Some of the materials deposited using the VAVD process include pure metals such as aluminum, chromium, gold, molybdenum, nickel, silver, stainless steel, titanium and tungsten. Commonly used alloys include stainless steel, nickel-chromium, lead, tin and Mxe2x80x94Crxe2x80x94Alxe2x80x94Y. Typical compounds used in the process include Al2O3, TiC and TiB2.
The present invention overcomes many of the drawbacks and disadvantages of known marking methods and similar thin film deposition devices. One object of the preferred embodiment is to provide a means to clean and prepare a surface prior to applying a thin film deposition identification marking. The cleaning device preferably utilizes a high frequency generator and a cathode ring in close proximity to the part surface. This cleaning method removes contaminants and oxides from the area that will contain the identification mark.
In another use of the present invention, a matte finish thin film coating is applied to a surface, the area of which is limited to the size of the desired mark, to reduce the amount of glare radiating from a surface, thereby improving the readability of a machine-readable symbol using optical readers.
In still another use of the present invention, a thin film of clear metal can be deposited over an identification mark, the area of which is limited to the size of the desired mark, to provide protection from adverse environmental conditions.